This invention relates to a device to aid the orientation of blind and partially sighted people.
Blind or partially sighted people usually use a cane (so-called mobility cane or long cane) for orientation, with which objects in a distance up to 1.2 m can be detected. The orientation with such a long cane has several disadvantages. For example, objects cannot be detected if they are not located near the ground and within a distance of about 1.2 m. The head and the breast area of the blind person cannot be protected. Objects in this height are often recognised to late which often result in hurting the blind person.
A number of devices for blind or partially sighted people is known which use contactless distance measurement systems to overcome the disadvantages of the long cane. Different versions of such a contactless distance measurement system are known. These devices comprise a transmitter which sends out a measurement beam and if the beam is reflected by an object a receiver detects the reflected beam. The distance between the device and the object is determined either by time of flight measurement, phase modulation measurement or by triangulation measurement. The measurement beam can be electro-magnetic (IR-radiation or laser beam) or sonic. The determined distance will be converted into a distance-dependent correcting variable which will be supplied to an indicator that displays the distance in a way that is adapted to the needs of the blind and partially sighted persons. Such indicators use either acoustic or tactile signals.
Furthermore, long cane are known, which are provided with an additional device comprising a contactless measuring system by means of which space ranges are detected, which cannot be detected by the long cane itself. The beam lobe of the measuring system is directed in the walking direction and considerably exceeds the range of the long cane. Due to the extended beam lobe (particularly when using ultrasonic devices) such additional devices detects a large space area. When an object is detected in this space area, a warning signal is supplied to the blind person.
It has been found that known contactless measuring devices, regardless whether they arc used in combination with a long cane or not, have disadvantages which make them very uncomfortable in use. The known devices generate warning signals or distance signals for indicating objects which are not located in the range relevant for the blind person. The user receives a large amount of signals which are very hard to interpret and which disturb the orientation of the blind person.
The object of the present invention is hence to provide a device to aid the orientation of blind and partially sighted people, by means of which device the head and breast area of the blind person is protectable without supplying unnecessary signals.
According to the invention, this object is achieved by a device comprising a cane, and further comprising measuring means comprising laser source means generating laser beams and laser light detecting means responding to laser light from said laser source means, said laser source means and said laser light detecting means being arranged to define a planar detection area in a detection plane comprising said cane, and indicating means for indicating the presence and the absence of an object in said planar detection area by a first and a second information, respectively.
The invention is based on the realization that the use of a device to aid the orientation of blind people is acceptable to the blind person only if the information signals concerning an obstacle can be interpreted without further considerations. Most of the blind persons are used to the long cane and even trained in use of such a long cane.
The device according to the present invention does not replace the long cane but is a combination of a long cane and an additional device comprising measuring means and indicating means. The operation of the additional device is such that it xe2x80x9csimulatesxe2x80x9d the use of the long cane. This is effected in that the additional device only detects a determined area (xe2x80x9cplanar detection areaxe2x80x9d) in a determined plane (xe2x80x9cdetection planexe2x80x9d). This plane is selected such that it comprises the long cane When the blind person moves the long cane in usual manner laterally to the left and to the right in order to scan the ground with the tip of the long cane, then the space above the long cane is detected by the additional device in such a manner that only a two-dimensional area above and in the prolongation of the long cane is detected. The additional device indicates the presence of an object in this planar area by providing a first information as well as the absence of an object in this planar detection area by providing a second information. The first information can, for example, be constituted by the presence of a particular (acoustic or tactile) signal and the second information can be constituted by the absence of a particular (acoustic or tactile) signal, or vice versa. The effect of this scanning is similar to the effect of scanning this space by the long cane itself, that means if the blind person could move the long cane to the left and to the right and simultaneously move it up and down. (Such a simultaneous movement of the long cane is, of course, not possible.) By this functional similarity with the function of the long cane itself, the device according to the invention does not require any training.
The principle of the measuring means used in the present invention for detecting objects in the planar detection area could be any known contactless operating principle used for measuring distances, for example the principle of time of flight measurement, the principle of triangulation measurement or the principle of phase modulation measurement. Such principle are known per se and therefore not described in detail herein.
In a preferred embodiment of the invention the measuring means operate according the principle of time of flight measurement of laser pulses. In this embodiment the laser source means are formed by laser pulse generating means for generating laser pulses. The laser light detecting means are formed by photodetector means responding to the laser pulses generated be the laser pulse generating means and reflected by an object in the planar detection area. Furthermore, signal processing means are provided. These signal processing means determine the duration between generating or sending a laser pulse by the laser pulse generating means and detecting this laser pulse by the photodetector means in relation to a predetermined duration. The laser pulse generating means can comprise one single laser source or several laser sources as well as the photodetector means can comprise one single photodetector or several photodetectors.
One possibility to arrange the measuring means to define a planar detection area exclusively in the selected detection plane can be achieved by generating several laser beams which all are located side by side in this detection plane. The number of laser beams and the closeness will then depend on the desired accuracy of detection.
A further possibility to arrange the measuring means to define a planar detection area exclusively in the selected detection plane can be achieved in that the generated laser beams are deflected by beam deflection means such that the beams are deflected in the planar detection area. Such beam deflection means can be means which either changes the direction of a beam or which deflects the beam such that the divergence of the beam is varied, for example increased in one direction or decreased in another direction to fan out the hewn. These beam deflection means can comprise, for example, an oscillating mirror which periodically deflects laser beams, for example, from one single laser source such that the two-dimensional detection area is scanned by the deflected laser beam. The beam deflection means can also comprise other beam deflection components as, for example, a prism. As mentioned above, the beam deflection means can be Laser beam divergence influencing means by which the divergence of the laser beams generated by said laser source means is increased two-dimensionally, that means in the detection plane, or decreased in a plane perpendicular to the detection plane. Such laser beam influencing means are known and can, for example, comprise a lens system having cylindrical lenses. Such beam divergence influencing means effect the laser beam to fan out in one plane and to cover an area, the extension of which depending on the extension of the angle of divergence of the beam. By using such beam divergence influencing means the planar detection area can be covered by one single laser beam having increased divergence, instead of several individual laser beams. Furthermore, this ensures that the entire planar detection area is simultaneously covered by laser radiation.
Advantageously, the device comprises limiting means for restricting the planar detection area such that the planar detection area is defined by determined limits. These limit can be defined as a function of the length of the long cane, of the extension of the long cane and of the height of the blind person using the device. Limit varying means can be provided for varying these limits of the planar detection area. These limit varying means can be used in order to individually adapt the desired planar detection area to individually different heights or individually different desires concerning the extension of the planar detection area
At least one of the limits of the planar detection area can be determined by fixed or variable beam limiting means for limiting the laser beams. Such beam limiting means can, for example, be beam divergence limiting means such as filters, stop means, diaphragms or lenses, for example a cylindrical lens. The limits can be varied, for example, by replacing the lens system by another lens system having other properties with respect to the achieved beam divergence.
Furthermore, at least one of the limits of the planar detection area can be determined by time range means for defining a fixed or variable time range for detecting the laser pulses by the photodetector means. The time range can be varied by varying the time constant of a RC-network using, for example, a potentiometer. This time range can be triggered by the laser pulse generated by the laser pulse generating means. If the duration between generating the laser pulse and detecting the laser pulse is shorter than this time constant, then the object reflecting the laser pulse is located within this limit of the planar detection area. If, however, the duration between generating die laser pulse and detecting the laser pulse is longer than this time constant, then the object reflecting the laser pulse is located beyond this limit of the planar detection area.
If the long cane and the additional device is rotated or inclined, then the detection plane of the planar detection area is inclined relative to the vertical plane. This can be done on purpose in order to scan objects located laterally from the long cane. However, this tilting can be done by mistake and the blind person still thinks that the detection plane of planar detection area is vertical. In order to avoid this, inclination sensor means can be provided for determining the inclination of the detection plane of the planar detection area relative to a vertical plane. These inclination sensor means can be arranged to define a threshold angle and to generate a sensor signal when the detection plane of the planar detection area is inclined by more than this threshold angle relative to a vertical plane. This signal can be a warning signal generated by inclination indication means in the form, for example, of a tone generator indicating to the blind person that the detection plane is not aligned with the vertical plane. The amount of the inclination triggering the warning signal is determined by the threshold angle. It could be useful to define a time period between exceeding the threshold angle and generating the warning signal such that, for example, no warning signal is generated when the detection plane is inclined for only a short time in order to scan objects located laterally from the long cane. The signal generated by the inclination sensor means can also be a control signal for controlling the additional device to rotate the detection plane into the vertical plane or for turning off the laser source means.
However, the inclination indicating means can also be represented by a perceptible feature provided on the long cane or on the additional device. This perceptible feature can be an asymmetric handle of the long cane. In this case, the blind person knows in which direction the detection plane is pointing just by holding this handle in his hand.
The measuring means, the indicating and/or the inclination sensor means can be provided on the long cane in different manner. For example, they can be accommodated in a common housing or in individual housings. This or these housings can be integral with the long cane, for example be an integral part of the handle. However, the hosing or housings can also be attachable to the long cane by means of attachment means (for example screws or the like). In this way it is possible to provide an already existing long cane with the additional device defined herein.
Further objects and features of the invention will be apparent to a person skilled in the art from the following specification of a preferred embodiment when read in conjunction with the appended claims.